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go-read-var-log

REST /var/log reader

Contents

Assumptions

Some assumptions could be considered TODO items for future enhancement

  • The log files are in /var/log
  • The log files are uncompressed plain text files
    • Compressed or archived files (e.g. .gz, bz2, .tar, .tgz) are not supported
  • The log files are sorted by timestamp (oldest first) as it is captured in each log event
  • Log events are separated by a newline character
  • REST response Content-Type is text/plain; charset=utf-8, regardless of the Accept request header
  • All errors are returned to REST callers as HTTP status 500, even if these might be correctable by the caller
  • LRU result caching of compiled regexes and search results are not implemented
    • Search result caching would require invalidation when the file changes
    • Hot searches could have dedicated caches that are eagerly refreshed when the file changes
  • Testing coverage should be added for the controller package
  • Add GOMAXPROCS to Dockerfile or set that in the code
  • There is a get-large-log branch where I hope to experiment with a more efficient way to read very large files, but it is not yet complete and is not formally part of this submission

Endpoints

  • GET /api/v1/logs - Get list of all log files in /var/log that this service can read
  • GET /api/v1/logs/{log} - Get the contents of the log file specified by {log} in /var/log (e.g. /api/v1/logs/system.log)
    Query Parameters:
    • n - Number of lines to return (default: 25, all: 0)
    • q - Case sensitive fixed text filter to apply to each line (default: ""), more performant than r
    • r - Regex filter to apply to each line (default: .*)
    • Note: q and r may both be specified, but at most once each. Multiple q or r parameters are ignored.

Enabling Tech Stack

  • Go - Programming language
    • If not installed, consider: brew install golang or similar as appropriate for how you manage packages for development on your OS
    • Installation is not required if running in Docker
  • HttpRouter - HTTP request router

Design

  • The service package contains the logic of the service, agnostic of presentation and transport
  • The controller package contains the HTTP request handlers

Generation of Sample Input Log Files

Optionally, arbitrarily large fake log files can be generated in json or delimited format to augment any that are naturally in /var/log.

Arguments

Argument Description
-h | --help Print the help message
-l Large File Bytes (default 10,000,000)
-lt Log with timestamps (UTC)
-n Number of lines to return (default 25)
-p HTTP Port to listen on (default 8080)

Running in Docker

  • docker build -t go-read-var-log . - Build the Docker image
  • docker run -v /var/log:/var/log:ro -p 80:8080 go-read-var-log <args> - Run with the given arguments
    Prevents writing to /var/log. When run without <args>, this enables the following from the docker host:
    • curl "localhost/api/v1/logs"
    • curl "localhost/api/v1/logs/system.log?n=10&q=syslog"

Running Locally

  • go run ./main <args> - Run the main.go file with the given arguments
  • IMPORTANT: Improve scalability with GOMAXPROCS: GOMAXPROCS=8 go run ./main <args>

Run Unit Tests Locally

Tests are implemented in *_test.go files in the same package as the code under test. Test data files are stored under testdata directories, which are ignored by go build and go run.

  • go test ./... -count=-1 - Run all unit tests
  • go test ./... -count=-1 -cover - Run all unit tests with coverage

Sample Output

Get list of all log files in /var/log

❯ curl "localhost/api/v1/logs"
1GB-9million.log
daily.out
displaypolicyd.stdout.log
fct_uninstall.log
fctinstallpost.log
fsck_apfs.log
fsck_apfs_error.log
fsck_hfs.log
install.log
monthly.out
output.log
shutdown_monitor.log
system.log
weekly.out
wifi.log

Query the contents of a 1GB file with 9.2 million logs

/var/log/1GB-9million.log was generated with GitHub mikebd/go-make-log.

❯ go run ./main -p 80
...
logs.go:31: /api/v1/logs/1GB-9million.log?q=error&r=\sfecig$&n=1 returned 1 lines using large strategy in 1.23877778s
logs.go:31: /api/v1/logs/1GB-9million.log?q=error&r=\sfecig$&n=1 returned 1 lines using large strategy in 1.202586854s
logs.go:31: /api/v1/logs/1GB-9million.log?q=error&r=\sfecig$&n=1 returned 1 lines using large strategy in 1.198800304s
logs.go:31: /api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1 returned 1 lines using large strategy in 856.594448ms
logs.go:31: /api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1 returned 1 lines using large strategy in 866.171423ms
logs.go:31: /api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1 returned 1 lines using large strategy in 863.319268ms

☝️ was generated by the following curl commands:

❯ curl "localhost/api/v1/logs/1GB-9million.log?q=error&r=\sfecig$&n=1" 
❯ curl "localhost/api/v1/logs/1GB-9million.log?q=error&r=\sfecig$&n=1" 
❯ curl "localhost/api/v1/logs/1GB-9million.log?q=error&r=\sfecig$&n=1" 
❯ curl "localhost/api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1" 
❯ curl "localhost/api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1" 
❯ curl "localhost/api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1"

The curl output for all of the above is:

2023-10-10T09:27:32.029729Z|error|tesak awehit atep itego anetar utiyav oset h om tulad palopi ac arinem eralo fecig

Benchmark with Apache Bench

Apache Bench is a simple HTTP load testing tool.

Small file

/var/log/daily.out is a 498KB file with 7,992 lines.

❯ ab -c 6 -k -n 10000 'localhost/api/v1/logs/daily.out'

Document Path:          /api/v1/logs/daily.out
Document Length:        1930 bytes

Concurrency Level:      6
Time taken for tests:   2.062 seconds
Complete requests:      10000
Failed requests:        0
Keep-Alive requests:    10000
Total transferred:      20730000 bytes
HTML transferred:       19300000 bytes
Requests per second:    4849.47 [#/sec] (mean)
Time per request:       1.237 [ms] (mean)
Time per request:       0.206 [ms] (mean, across all concurrent requests)
Transfer rate:          9817.34 [Kbytes/sec] received

Connection Times (ms)
min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:     0    1   0.3      1       3
Waiting:        0    1   0.3      1       3
Total:          0    1   0.3      1       3

Percentage of the requests served within a certain time (ms)
50%      1
66%      1
75%      1
80%      1
90%      2
95%      2
98%      2
99%      2
100%     3 (longest request)

Large file with fixed text and regex matching

Non-default GOMAXPROCS=8

❯ ab -c 6 -k -n 1000 'localhost/api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1'

Document Path:          /api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1
Document Length:        117 bytes

Concurrency Level:      6
Time taken for tests:   259.356 seconds
Complete requests:      1000
Failed requests:        0
Keep-Alive requests:    1000
Total transferred:      259000 bytes
HTML transferred:       117000 bytes
Requests per second:    3.86 [#/sec] (mean)
Time per request:       1556.135 [ms] (mean)
Time per request:       259.356 [ms] (mean, across all concurrent requests)
Transfer rate:          0.98 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:   909 1550  51.8   1541    1788
Waiting:      908 1550  51.8   1540    1788
Total:        909 1550  51.8   1541    1788

Percentage of the requests served within a certain time (ms)
  50%   1541
  66%   1559
  75%   1568
  80%   1578
  90%   1605
  95%   1632
  98%   1692
  99%   1757
 100%   1788 (longest request)

Default GOMAXPROCS=1

❯ ab -c 6 -k -n 1000 'localhost/api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1'

Document Path:          /api/v1/logs/1GB-9million.log?q=|error|&r=\sfecig$&n=1
Document Length:        117 bytes

Concurrency Level:      6
Time taken for tests:   279.119 seconds
Complete requests:      1000
Failed requests:        0
Keep-Alive requests:    1000
Total transferred:      259000 bytes
HTML transferred:       117000 bytes
Requests per second:    3.58 [#/sec] (mean)
Time per request:       1674.712 [ms] (mean)
Time per request:       279.119 [ms] (mean, across all concurrent requests)
Transfer rate:          0.91 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.0      0       0
Processing:  1276 1663  53.5   1654    2018
Waiting:     1276 1663  53.5   1653    2018
Total:       1276 1663  53.5   1654    2018

Percentage of the requests served within a certain time (ms)
  50%   1654
  66%   1667
  75%   1679
  80%   1687
  90%   1714
  95%   1745
  98%   1803
  99%   1932
 100%   2018 (longest request)